Coherent Population Trapping Resonances in Buffer Gas-filled Cs Vapor Cells with Push-Pull Optical Pumping

We report on a theoretical study and experimental characterization of coherent population trapping (CPT) resonances in buffer gas-filled vapor cells with push-pull optical pumping (PPOP) on Cs D1 line. We point out that the push-pull interaction scheme is identical to the so-called lin per lin polarization scheme. Expressions of the relevant dark states, as well as of absorption, are reported. The experimental setup is based on the combination of a distributed feedback (DFB) diode laser, a pigtailed intensity Mach-Zehnder electro-optic modulator (MZ EOM) for optical sidebands generation and a Michelson-like interferometer. A microwave technique to stabilize the transfer function operating point of the MZ EOM is implemented for proper operation. A CPT resonance contrast as high as 78% is reported in a cm-scale cell for the magnetic-field insensitive clock transition. The impact of the laser intensity on the CPT clock signal key parameters (linewidth - contrast - linewidth/contrast ratio) is reported for three different cells with various dimensions and buffer gas contents. The potential of the PPOP technique for the development of high-performance atomic vapor cell clocks is discussed.Comment: 28 pages, 12 figure

Characterization of Cs vapor cell coated with octadecyltrichlorosilane using coherent population trapping spectroscopy

We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 $\pm$ 0.03) eV, leading to a clock frequency shift rate of $2.7\times10^{-9}/$K in fractional unit. A hyperfine population lifetime, $T_1$, and a microwave coherence lifetime, $T_2$, of 1.6 and 0.5 ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed.Comment: 33 pages, 13 figure

Towards micro-assembly of hybrid MOEMS components on reconfigurable silicon free-space micro-optical bench.

International audienceThe 3D integration of hybrid chips is a viable approach for the micro-optical technologies to reduce the costs of assembly and packaging. In this paper a technology platform for the hybrid integration of MOEMS components on a reconfigurable free-space silicon micro-optical bench is presented. In this approach a desired optical component (e.g. micromirror, microlens) is integrated with removable and adjustable silicon holder which can be manipulated, aligned and fixed in the precisely etched rail of the silicon baseplate by use of robotic micro-assembly station. An active-based gripping system allows modification of the holder position on the baseplate with nanometre precision. The fabrication processes of the micromachined parts of the micro-optical bench, based on bulk micromachining of standard silicon wafer and SOI wafer, are described. The successful assembly of the holders, equipped with micromirror and refractive glass ball microlens, on the baseplate rail is demonstrated

Modular and Reconfigurable 3D Micro-Optical Benches : Concept, Validation and Characterization.

International audienceIn this paper, we present an approach to design MOEMS based on Reconfigurable Free Space Micro-Optical Benches (RFS-MOB). The proposed concept enables to design modular and reconfigurable MOEMS by using a generic structure of silicon holders and non defined position in the substrate. Various micro-optical elements, e.g. microlenses or micromirrors, can be integrated within holders. Their assembly is achieved with an active microgripper, after high precision alignement within guiding rails of silicon substrate. Flexible parts are used to maintain a final position. The concept is validated by successful assembly of holders. A characterization method of assembled holders is proposed and provides an accuracy better than 0.04 for an angle measurement

Assembly of 3D reconfigurable hybrid MOEMS through microrobotic approach.

International audienceMicro-assembly has been identified to be a critical technology in the microsystems technology and nanotechnology. Increasing needs of MOEMS (Micro- Opto-Electro- Mechanical Systems) for microsystems conducts to development of new concepts and skilled micro-assembly stations. This paper presents a 3D microassembly station used for the reconfigurable free space micro-optical benches (RFSMOB) which are a promising type of MOEMS. Designed parts of RFS-MOB are assembled by using the developed micro-assembly station. The flexibility of the micro-assembly station provides the possibility to manipulate a variety of microcomponents. The RFS-MOB design enables to reduce adhesion forces effects during releasing operations. Experimental results are shown and validate the effectiveness of the micro-assembly station and micro-assembly strategies

A micro-assembly station used for 3D reconfigurable hybrid MOEMS assembly - (Special Award).

International audienceMicro-assembly has been identified to be a critical technology in the microsystems technology and nanotechnology. The increasing needs of MOEMS (Micro-Opto-Electro- Mechanical Systems) for the microsystems conducts to development of new concepts and skilled micro-assembly stations. This paper presents a 3D micro-assembly station used for the reconfigurable free space micro-optical benches (RFS-MOB) which are a promising type of MOEMS. The designed parts of RFS-MOB are assembled by using the developped microassembly station. Experimental results are shown and validate the effectiveness of the micro-assembly station and the microassembly strategies

Quadratic dependence on temperature of Cs 0-0 hyperfine resonance frequency in single Ne buffer gas microfabricated vapour cell

Presented is the observation of a quadratic temperature dependence of the Cs 0-0 ground state hyperfine resonance frequency in a single Neon (Ne) buffer gas vapour microcell. The inversion temperature, expected to be theoretically independent of the buffer gas pressure, is measured to be about 80-C for two different samples. A proposal to develop chip scale atomic clocks with improved long-term frequency stability, simpler configuration (a single buffer gas instead of a buffer gas mixture) and then relaxed constraints on pressure accuracy during the cell filling procedure is presented

Laser light routing in an elongated micromachined vapor cell with diffraction gratings for atomic clock applications

International audienceThis paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation. Then, the length of the cavity where light interacts with alkali atoms can be extended. We demonstrate that a longer cell allows to reduce the beam diameter, while preserving the clock performances. As the cavity depth and the beam diameter are reduced, collimation can be performed in a tighter space. This solution relaxes the constraints on the device packaging and is suitable for wafer-level assembly. Several cells have been fabricated and characterized in a clock setup using coherent population trapping spectroscopy. The measured signals exhibit null power linewidths down to 2.23 kHz and high transmission contrasts up to 17%. A high contrast-to-linewidth ratio is found at a linewidth of 4.17 kHz and a contrast of 5.2% in a 7-mm-long cell despite a beam diameter reduced to 600 μm

Fabricación de sistemas MEMS – un caso de estudio en la fabricación de un micro-espejo

This paper presents the working principle, design, and fabrication of a silicon-based scanning micromirror with a new type of action mechanism as an example of MEMS (Micro-Electro-Mechanical Systems). Micromirrors can be found in barcode readers as well as micro-projectors, optical coherence tomography, or spectrometers’ adjustable filters. The fabrication process of the device prompted us to describe and discuss the problems related to the manufacture of MEMS. The article starts with some terminology and a brief introduction to the field of microsystems. Afterwards, the concept of a new scanning micromirror is explained. The device is operated by two pairs of thermal bimorphs. A special design enables to maintain a constant distance from the center of the mirror to the light source during the scanning process. The device was implemented in a one degree-of-freedom micromirror and a two degree-of-freedom micromirror. The fabrication process of both types is described. For each case, a different type of substrate was used. The first type of substrate was a standard silicon wafer; the second one, SOI (Silicon-On-Insulator). The process with the first one was complicated and caused many problems. Replacing this substrate with SOI solved some of the issues, but did not prevent new ones from arising. Nevertheless, the SOI substrate produces much better results and it is preferable to manufacture this type of MEMS devices.Este trabajo muestra un mecanismo de acción, un diseño y una fabricación de un nuevo dispositivo de escaneo - un micro-espejo. Los micro-espejos se pueden encontrar en los lectores de códigos de barras, así como en los micro proyectores, en sistemas de tomografía óptica coherente, o en los filtros ajustables de espectrómetros. El proceso de formación del nuevo dispositivo nos llevó a describir y discutir los problemas relacionados con la fabricación de MEMS (sistemas microelectrónicos). En primer lugar, se da una terminología y una breve introducción al campo de los microsistemas. A continuación, se explica un concepto del nuevo micro-espejo de escanéo. El dispositivo es accionado por dos pares de actuadores termo-bimorfos. Un diseño especial permite mantener la distancia constante desde el centro del espejo a la fuente de luz durante el proceso de escaneo. El dispositivo se implementó en dos versiones: un micro-espejo con un grado de libertad y un micro-espejo con dos grados de libertad. Se describe un proceso de fabricación para los dos tipos del dispositivo que utiliza dos tipos diferentes de sustrato. El primer tipo de sustrato corresponde a una oblea de silicio estándar, el segundo substrato corresponde a un SOI (Silicon-On-Insulator). El proceso con la oblea de silicio estándar fue complicado y causó muchos problemas. Cambiar el sustrato a SOI ayudó a resolver algunos de ellos, pero no permitió evitar algunos nuevos. Sin embargo, el sustrato SOI da mejores resultados y se encuentra que es preferible fabricar dispositivos MEMS de este tipo

Cross Absolute Filter for removing speckle noise from interference patterns

Abstract A new algorithm for speckle noise removal from interference patterns is proposed. The method, called Cross Absolute Filter (CAF), is especially well suited to the case of noisy interferograms with phase error pixels. Extensive computer simulations performed on both digitally generated fringes and experimental data show that CAF performs better than classical median-type filters, preserving more subtle details